There are existing devices that can accurately and efficiently detect and/or image infrared (IR) radiation. These devices are utilized in a variety of applications, including military and commercial applications. However, it is possible for environmental and other factors to interfere with efficient and accurate detection of a target or scene using IR energy. For example, the presence of clouds, smoke, rain, or even camouflage netting can make it difficult for an IR detector to accurately and reliably detect the IR radiation emitted from or scattered by a target or scene which is of interest. On the hand, a target or scene of interest will usually emit or scatter not only IR radiation, but also radiation at significantly lower frequencies. Radiation at these lower frequencies can readily penetrate clouds, smoke, rain, camouflage netting and other comparable conditions or structures, and is thus less susceptible to adverse influence from various environmental conditions. However, detecting and/or imaging this lower frequency radiation can present some problems.
In this regard, existing IR detectors (which are often called bolometers) are highly sensitive devices that are capable of measuring a temperature change caused by the absorption by the detector of received radiation. Although these devices are optimized for IR radiation, radiant energy in other frequency ranges can theoretically be absorbed and produce a measurable temperature change within an IR detector. This is advantageous from the perspective that, as noted above, radiation with a frequency well below the frequency of IR radiation is less susceptible to certain environmental influences.
Consideration has therefore been given to the idea of using an IR detector to detect such radiation. However, in the case of radiation with a frequency well below that of IR radiation, the wavelength of the radiation is much longer than the size of a typical bolometer. Consequently, in order to efficiently capture the energy of this radiation, it is necessary to provide a resonant antenna-like structure for the low frequency radiation. In this regard, in order to efficiently detect lower frequency radiation through use of an antenna, the electromagnetic energy received by the antenna must be efficiently coupled into the IR detector, so that the IR detector undergoes a measurable temperature change.
But optimized bolometers usually have a thermally sensitive material (such as amorphous silicon) with an electrical resistance which is several thousand ohms per square. This resistance would also correspond to the electromagnetic load resistance presented by the bolometer to the antenna. In contrast, resonant antenna configurations suitable for the low frequency radiation of interest will typically have a relatively low impedance, on the order of a few ohms to a few hundred ohms. Therefore, the concept of using a resonant antenna-like structure with a bolometer has been hampered by the fact that the need to maximize the sensitivity of the high-resistance bolometer tends to conflict with the need to match the bolometer impedance to the low-impedance antenna resonator.